1. Field of the Invention
The present invention relates to an engine starter having a starter motor that includes a field coil for generating a magnetic field.
2. Description of the Related Art
JP-A-Hei 3-37373 discloses such an engine starter. Usually, a starter motor has a series-wound field coil and a parallel-wound field coil. A control element is connected in series to the parallel-wound field coil to control current supplied to the parallel-wound field coil by a control circuit. When the starter is operated, current supplied by a battery to the starter motor increases according to the time constant of the power supply circuit of the starter motor to rotate the crankshaft of an engine. The amount of the current that is supplied to the starter motor becomes maximum when the crankshaft starts its rotation and, thereafter, gradually becomes smaller due to a counter electromotive force generated in the armature of the starter motor.
Because the amount of current supplied to the starter motor is very large when the crankshaft starts rotation, terminal voltage of the battery becomes very low, so that various electrical accessories of a vehicle may not operate properly.
On the other hand, when the starter is connected to the engine, a pinion of the starter and a ring gear of the engine may make big noises if electric current supplied to the starter motor is too large. Such a large amount of electric current may cause sparks between brushes and a commutator of the starter motor and shorten the life time thereof.